Electromechanical latching actuator

ABSTRACT

An electromechanical latching actuator for producing linear or rotary motion. The device includes one or more sets of permanent magnets and electric coils which annul and flux switch a magnetic field between adjacent magnetic poles thereby sequentially generating a force or torque that can be coupled to a suitable load. A fluid valve coupled to such actuator.

United States Patent [191 Benson [4 1 Nov. 13, 1973 ELECTROMECHANICALLATCHING ACTUATOR 3,119,940 1/1964 Pettit et a1. 310/24 [75] Inventor:Glendon M. Benson, Danville, Calif. primary Examiner (;erald Goldberg[73] Assignees New Process Industries, Inc., Atwmey stephen Townsend etMinneapolis, Minn.

[22] Filed: July 19, 1972 21 Appl. No.: 273,062 [57] ABSTRACT Anelectromechanical latching actuator for producing 1 1 Cl 310/34 linearor rotary motion. The device includes one or [51] Int. Cl. H02k 41/00more sets of permanent magnets and electric coils 1 1 Field seal'dlwhich annul and flux switch a magnetic field between 156 adjacentmagnetic poles thereby sequentially generating a force or torque thatcan be coupled to a suitable 1 Referelwes Cited load. A fluid valvecoupled to such actuator.

UNITED STATES PATENTS 3,022,450 2/1962 Chase, Jr. 310/30 X 16 Claims, 16Drawing Figures J x @56" f e PAIFNIEI] IIUY I 3 I973 SIIEEI 15? 6 n .v 8x x Q I FIG. IA.

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ELECTROMECI-IANICAL LATCHING ACTUATOR This invention relates toapparatus that sequentially generates a latching or a driving force ortorque by switching or nullifying the magnetic flux generated byperpendicularly poled permanent magnets by meanS of reversing themagnetizing force generated by one or more electric coils.

In process and machine control systems it is often beneficial to producea torque or force in discrete steps wit non-mechanical latching betweeneach step. It is further desirable to produce a given torque or forcewith a most compact, lightweight mechanism, having fast response, highefficiency and positional accuracy and in addition a deivce that ispassive during latching. It is further desirable that such Mechanism bebi-stable for digital control and not employ moving electric coils whichrequire brushes and flexible conductors to effect connection to thecoils. The present invention meets these requirements and can be variedin configuration and function to match a wide range of outputrequirements.

Broadly stated the present invention relates to an actuator or steppingmotor that produces bi-di'rectional forcing and latching by aperpendicularly poled permanent magnet that functions without polarityswitching and produces bi-directional movement in cooperaton withelectrical coils that are pulsed with alternating polarity.

These coils switch and augment the magnetic flux generated by thepermanent magnet between opposite air-gaps in which a mechanical forceis generated by the flux at these air-gaps. Since the effective air-gaplength changes during movement, the reluctance of each magnetic circuitchanges, and as a result these actuators or stepping motors may beclassed as latching, variable reluctance, multiple-pole types withperpendicularly poled permanent magnets.

The principal fetures of this invention include: (1) bi-stable operation(the actuator remains position locked at each increment of movement withmagnetic flux acting as the holding force); (2) bi-directional operation(the acutator has force symmetry for moving and latching, requiring onlyreversal of voltage polarity to effect movement); (3) passive latching(no electrical power is consumed for position holding), (4) squarewaveforce response (the actuator can develop a constant force throughout thedisplacement which equals the latching force, and the latching force canbe made independent of air-gap length over a prescribed air-gap range'owing to magnetic core saturation; (5) high force capability (theactuator can develop up to 24 kilogauss flux across an air-gap duringlatching and moving, corresponding to a mechanical unit force of 332pounds per square inch of air-gap face cross-sectional area); and (6)flexibility of design (permits the use of a range of permanent magnetmaterials and coil geometries, including both wire and tape wound, whichpermits tailoring the actuator to meet cost, performance, and electricalrequirements).

Examples of design flexibility include: (I) for low cost and performancethe use of ceramic permanent magnets and ingot iron or silicon steelmagnetic cores and tape wound coils; (2) for intermediate cost andperformance the use of Alnico 8 permanent magnets and silicon steelmagnetic cores and tape wound coils; and (3) for high cost andperformance the use of rare earth cobalt permanent magnets andSupermendur magnetic cores and wire wound insulation encapsulated coils.Each of these design examples is capable of saturating the magnetic coreat the air-gap pole faces since the magnetic area of the permanentmagnet is considerably larger than at the poles or in the connectingmagnetic circuit.

.Another aspact of the present invention is directed to a latchinglinear or rotary actuator that produces bidirectional forcing andpassive latching by a perpendicularly poled permanent magnet having ashort magnetic length anda large magnetic area that functions withoutpolarity switching and produces bi-directional movement by electricalcoils that are pulse energized with alternating polarity. These coilsswitch and augment the magnetic flux generated by the permanent magnetbetween parallel magnetic circuits in which a mechanical force isgenerated on a movable element and subsequently applied to movablevalving elements of fluid control devices for the control of fluid flow.The present invention provides high forces generated by the high fluxdensitites produced by the permanent magnet configuration whichminimizes current and electrical power requirements and simplifies thecontrol logic required.

The foregoing, together with other objects, features and advantages ofthe present invention will become more apparent after referring to thefollowing specification and accompanying drawings in which:

FIGS. lA-lD depict an embodiment of the invention in various states ofoperation thereof;

FIG. 2 is an elevation view in cross-section of an embodiment of thepresent invention employed for driving a fluid valve;

FIG. 2A is a top view of the device of FIG. 2;

FIG. 2B is a fragmentary cross-sectional view taken along line BB ofFIG. 2;

FIG. 2C is a fragmentary cross-sectional view taken along line CC ofFIG. 2;

FIG. 3 is a cross-section elevation view of another embodiment of thepresent invention;

FIG. 4 is an elevation view in cross-section of still another embodimentof the present invention;

FIG. 5 is an elevation view in cross-section of a rotary actuatoraccording to the present invention;

FIG. 5A is a sectional view taken along line 5A--5A of FIG. 5;

FIG. 6A is a cross-sectional view of another rotary actuator accordingto the present invention;

FIG. 6B is a cross-sectional view taken along line BB of FIG. 6A;

FIG. 6C is a view taken along line CC of FIG. 6A; and

FIG. 7 is a schematic diagram of an electric control circuit suitablefor controlling the actuators of the present invention.

Referring more particularly to the drawings and specifically FIGS.lA-lD, reference numeral 12 indicates a magnetic plunger which isattached to an actuator rod 14. The actuator rod is supported forreciprocal movement in housing 15 composed of magnetic housing segmentsor core cups 15A and 158. Also attached to magnetic plunger 12 is apermanent magnet 16 of annular form and a magnetic tube 18 which is alsoannular and circumscribes permanent magent 16. Housing segments 15A and15B are retained in the position shown in the drawings by a non-magneticshell 20. The non-magnetic shell isolates housing segments 15A and 158from one another. Rigidly mounted within housing is a first coil 22 anda second coil 24. Coil 22 circumscribes the upper end of magneticplunger 12 and coil 24 circumscribes the lower end of the magneticplunger. Suitable terminals for the coils extend through housing members15A and 153 in a conventional manner and are therefore not shownspecifically in the drawings. Permanent magnet 16 is radially poled, bywhich is meant that one magnetic pole (e.g., North) is on the innercylindric surface of the permanent magnet and the other pole (e.g.,South) is on the outer cylindric surface so that the path of fluxproduced by the magnet is as shown by broken lines 26 in FIG. 1A.

In the configuration shown in FIG. 1 the load, attached to the lower endof the rod, is not shown. Alternately, the load could be attached to theupper end or both ends of the rod, or to the plunger itself. In FIG. 1Athe actuator is shown in the stable lower latched position. In thisposition the load absorbs the latching force of the actuator and a smallair-gap exists between the pole faces to accommodate any axialdeformation of the load without the pole faces bottoming out. Thelatching is produced by the magnetic field (shown by the dashed lines 26in FIG. 1A) generated by the radially poled permanent magnet 16 locatedin the plunger. The magnetic field is confined primarily to the lowermagnetic circuit, as shown, since the reluctance of the two upperair-gaps (between plunger and upper core) is large relative to thereluctance of the two lower air gaps. Magentic flux densities of 24 KGhave been obtained in the air-gaps (pole faces) in this latchingposition. These flux densities are high enough to saturate even advancedalloy cores. As a result of saturation, the latching force is nearlyindependent of lower air-gap clearance variations introduced bymanufacturing tolerances. As a result, the permanent magnet acts as avery strong spring which holds the integral plunger and actuator rod inthe down position. The relatively large diameter-to-length ratio of theplunger provides large stiffness which minimizes plunger flexure. Theactuator rod-ends can be lapped to sleeved bores of the core to provideprecise alignment and guidance and minimize friction.

The operation of the invention can be appreciated by following thesequence of positions depicted in FIGS. lA-lD. In FIG. 1A with coils 22and 24 disconnected from any power source, the movable member of thedevice composed of magnetic plunger 12, actuator rod 14, permanentmagnet 16 and magnetic sleeve 18 resides in the lower position, shown inFIG. 1A. The movable member is there retained because of the latchingflux path designated by broken lines 26. To switch or shift the movablemember upward to the opposite end of the casing a current pulse isdelivered to coils 22 and 24 which coils are typically series connected.The current pulse, generated for example by discharging a capacitorthrough an SCR, produces a magnetic field in upper core 15A and theupper part of plunger 12 as shown by the arrows in FIG. 1B andidentified by reference numeral 28.

This magnetic filed has the same direction as the magentic fieldproduced by permanent magnet 16 and consequently reinforces the magneticfield in the upper portion of plunger 12. The current pulse in lowercoil 24 produces a magnetic field in the lower portion of plunger 12which, as shown by the arrows in FIG. 1B, opposes the magnetic fieldproduced by permanent magnet 16 and nulls the magnetic field in theair-gap between plunger 12 and lower housing member 158. As a result nomagnetic field exists at the latter air gap while the air gap betweenplunger 12 and housing member 15A has a magnetic field density that islimited only by the saturation characteristic of the plunger. The areaof the movable portions of the structure is approximately one half thetotal half cross sectional area of the actuator, with one half of thepole area located between sleeve 18 and the housing and the other halfbetween plunger 12 and the inner surfaces of the housing member 15A or158. In order to achieve high flux densities at these air gap faces, themagnetic circuit has a nearly uniform cross-sectional area throughoutits magnetic length, the separation distance between the inner and outergaps is maximized, and the length to diameter ratio of the magnetichousing segments 15A and 15B are less than unity. This length todiameter ratio is achieved by providing coils 22 and 24 that are largerin a radial direction than they are in an axial direction.

The combination of a large core face or air-gap area and a high fluxdensity, produced by both the coil and the permanent magnet, leads to ahigh force actuator. The nulling of the magnetic spring force byenergization of coil 24 increases the force available for moving plunger12 and the parts attached thereto. The nulling effect, which fluxswitches the permanent magnet flux in actuator 12, is sufficient to movethe armature assembly without energizing coils 22 although energizationof the latter coil produces a faster acting movement of rod 12 and theload that is attached thereto.

As the armature moves upward as shown in FIG. 1B, the magnetic fieldproduced by the permanent magnet increases in the upper air-gap due tothe decrease in the air-gap and the consequent decrease in reluctance ofthe upper magnetic circuit. As the plunger 12 latches in the upperposition that portion of the magnetic energy which is produced by thecoils can be recovered by resonant charging of a capacitor in ananalogous manner to that of an LC resonant electric circuit. As a resultthe only appreciable electrical energy loss is that due to coilresistance. (The loss due to magnetic hysteresis and eddy currents isnegligible due to the design of plunger 12, sleeve 18 and housingmembers 15A and 15B and the method of operation.) The remainingelectrical energy is either converted to mechanical work (available atactuator rod 14) or recovered by recharging a suitable low passcapacitor (not shown). Upon completing the actuation cycle power isdisconnected from coils 22 and 24 and the actuator is passive, i.e., theplunger is latched in a position shown in FIG. 1C by the magnetic fluxpath indicated in such figure by the broken lines 26. The latching forceis provided solely by the magnetic field produced in the upper airgapsby the permanent magnet. The magnetic field in the lower air-gaps isnegligible due to much larger reluctance caused by these longerair-gaps. Since the mechanical force produce by a magnetic field isproportional to the square of the field density, the downward force isinsignificant. The magnetic flux shown by lines 26 in FIG. 1C isessentially confined to the upper housing member 15A, the plunger 12 andthe sleeve 18 and the flux direction through the permanent magnet 16 isthe same as that shown in FIG. 1A. As a result, the polarity of thepermanent magnet is not switched in going from one latched position tothe other and therefore the hysteresis loss and any demagnetizingeffects in the permanent magnet are minimized or virtually eliminated.

To move the plunger from the upper latched position of FIG. 1C, acurrent pulse is again supplied to coils 22 and 24. The direction of thecurrent is opposite from that referred to above in connection with FIG.1B and is indicated by arrows 28 in FIG. 1D. The current in coil 22creates a field in plunger 12 that bucks or nulls the flux resultingfrom the presence of permanent magnet 16. The current in coil 24generates a magnetic field in the lower air-gaps which reinforces oradds to the field produced by permanent magnet 16. As a result thespring force produced by the permanent magnet is nulled and the entireforce produced by the magnetic flux at the lower air-gap is available atactuator rod 14 and the load attached thereto. The magnetic flux at thelower air-gaps is sufficient to saturate the lower portion of plunger 12and lower housing magnetic member 15B. This force drives the actuatorrod 14, plunger 12, permanent magnet 16 and sleeve 18 downward. Themagnetic energy may again be recovered through resonant charging of acapacitor andthe system has returned to its latched position shown inFIG. 1A.

The embodiment of the invention shown in FIG. 1 can be designed suchthat the maximum energy product of the permanent magnet is attained atthe lower latched position. Under actuation the coil which reinforcesthe flux increases the magnetization level of the permanent magnet. As aresult the magnetic field produced by the reinforcing coil (e.g., coil24 in FIG. 1D) contributes on the average about one half of the totalflux while the permanent magnet contributes the other half. Due to thisflux switching operation the permanent magnet is not degraded inoperation as is the case in devices operated in flux opposition, but thepermanent magnet retains its high stability toward temperature andradiation effects.

The embodiment shown in FIG. 1 permits the use of a range of permanentmagnetic materials and coil sizes which allows tailoring the design tomeet the cost and performance requirements. This flexibility in designis due to three factors. One, the permanent magnet is never operatedmuch below its maximum energy product since the reinforcing field alwaysincreases the magnetization. Two, the radial thickness of the permanentmagnet can be altered to meet coercive strength requirements and theheight (and therefore the area) can be established to meet magnetizationrequirements necessary to achieve a prescribed flux density at theair-gaps. Three, pole profiling such conical pole faces, permitstailoring the force-displacement characteristic of the device.

FIG. 2 discloses an alternate embodiment of the present inventionincorporated in a valve structure. The modified structure includes aplunger 32 of magnetic material which is supported for axial movement onan actuator rod 34. Actuator rod 34 has attached to the lower endthereof a valve body 36 through a sleeve spring 38 which will bedescribed in more detail hereinafter. The housing for the structure isformed by an upper cylindric sleeve 40 and a lower cylindric sleeve 42,both of which are formed of magnetic material and joined to one anotherat a central seam 44. In the upper end of the housing and attached tothe upper end of sleeve 40 is an end flange 46 which is formed ofmagnetic material and has a central opening in which is supported amagnetic insert 48 which is formed of suitable magnetic material. Insert48 is centrally bonded to support actuator rod 34 for axial movementwithin the housing. The lower end of the housing is formed by a lowerend flange 50, constructed of suitable magnetic material and centrallybored to support the lower end of the actuator rod for axial movementwithin the housing. Rigidly mounted within the housing is a radiallypoled permanent magnet ring 52 in the interior opening of which issupported a cylindric magentic member 56. The axial ends of cylindricmagnetic member 56 are excised to receive therein non-magnetic end tubes58 and 60 which afford rigidity to the structure and form guides forplunger 32. Circumscribing non-magnetic end tube 58 is an electric coil62 and circumscribing non-magnetic end tube 60 is an electric coil 64.The coils are preferably connected in series. Coil terminal pins 62T and64T extend through upper flange 46 for effecting connection of the coilsto external circuitry.

Attached rigid with lower flange 50 is a valve plate 66 which defines aninlet passage 68 and an outlet passage 70. The inner end of outletpassage 70 defines a valve seat 72 which cooperates with valve body 36to arrest flow between the inlet and outlet passages when valve body 36is seated against the seat. For indicating the position of valve body 36with respect to seat 72, the upper end of the structure includes amechanism 73 for indicating the position of the valve.

Position indicator 73 includes a pair of Belleville spring washers 74which are mounted on the upper end of actuator rod 34 by a suitableretaining cap 76. The approximate radial extent of washer 74 is shown bybroken lines 75 in FIGS. 28 and 2C. Insert 48 is centrally bored todefine a chamber 78 in which the position indicating mechanism ishoused. The chamber is closed at the top by an insulative insert 80which supports terminal pins 82, 84 and 86. The terminal pins are spacedfrom the center of chamber 78 by an equal amount and are spacedcircumferentially uniformally around the insulative insert. Theterminals are radially spaced from the center of chamber 78 by'adistance greater than the outside diameter of washers 74. The lower endsof the terminal pins are supported by an insulative disc 88 which issuitably mounted in the inner end of chamber 78. The latter insert isbored at 89 to admit the upper end of actuator rod 34 between the twoinsulative inserts. Mounted on the lower surface of upper insert 80 is acontact 90 which is electrically connected to terminal pin 82. A contact92 is electrically connected to terminal pin 84.

Mounted on the upper surface of insulative disc 88 is a contact 94 whichis electrically connected to terminal pin 82 and a contact 96 that iselectrically connected to terminal pin 86. As can be seen in FIGS. 28and 2C contacts 90, 92, 94 and 96 extend radially inward from therespective terminal pins so that they are contacted by washers 74. Whenthe valve is in an open position, the position shown in FIG. 2, washer74 bridges contacts 90 and 92 so that the circuit is established betweenterminal pins 82 and 84. When the valve is closed washer 74 bridgescontacts 94 and 96 so that a circuit is completed between terminal pins82 and 86. Conventional circuitry can be connected to terminal pins 82,84 and 86 so that electrical response to the position of the valve canbe achieved.

As will appear valve body 36 is moved into the closed position againstseat 72 by movement of plunger 32 to a downward position against thesurface of lower falnge 50. Spring 38 compresses in such position sothat tolerances of construction and fabrication are not critical. Thespring is formed by a cylinder of suitable spring steel or the like thathas the appropriate resiliency characteristic. Pairs of diametricallyspaced excisions 98 are formed in the cylinderic wall of the spring,each pair being displaced 90 from the pair axially adjacent thereto. Theresultant spring while having sufficient resilience to assure positiveclosure of the valve has substantial stiffness so that the valve willnot bounce even though the entire structure may be subjected tovibrational forces.

Mounting of the device can be accomplished in any suitable way such asby placing the valve in a mating socket formed in a block designatedfragmentarily and in phantom in FIG. 2 by reference numeral 100. Thesocket includes a threaded opening 102, and a threaded ring 104 hascorresponding threads so that as the ring 104 is threaded into opening102 the structure is retained in place. Ring 104 is provided with meansfor gripping and turning the ring such as spanner wrench openings 15.Depending from the apparatus are two diametrically opposed anti-rotationpins 106 which enter corresponding openings in block 100. Finally, theblock is provided with a port 108 that registers with inlet port 68 ofthe apparatus and a port 110 that registers with the outlet port of theapparatus, a gasket 112 being placed so as to seal the ports.

The operation of the apparatus of FIG. 2 is as follows: With plunger 32in the position shown in FIG. 2, the plunger is latched in an upwardposition, corresponding to the open position of valve body 36, by fluxproduced by permanent magnet 52 which flows as indicated by the brokenline through magnetic insert 48, flange 46, and sleeve 40.

In the open position, an electrical circuit path is formed betweenterminals 82 and 84 so as to give an electrical indication of theposition of valve 36. When it is desired to seat valve 36 against seat72, thereby to interrupt the flow of fluid from inlet port 68 to outletport 70, a suitable electric pulse is supplied to terminal 62T and 641.The internal connections of coil 62 and 64 are such that the magneticfield produced in response to energization of coil 62 opposes the fluxindicated by the broken line in FIG. 2 so as to neutralize or nullifythe latching flux. Simultaneously coil 64 is energized so as to producean electromagnetic field that adds to the field produced by permanentmagnet 52 in a direction that causes plunger 32 to move downward towardlower flange 50. When the plunger reaches its downward most position,valve 36 seats against seat 72, spring 38 is compressed, and the plungeris latched in a lower or closed condition by the flux produced frompermanent magnet 52, which flows through cylindric member 56, plunger32, the lower air gap, lower flange 50, and lower'cylindric housingsleeve 42. The valve remains in a closed position even afterdisconnection of current from terminals from 62T and 64T. When it isdesired to open the valve, a current pulse of opposite polarity isapplied between terminals 621 and 64T and the latching flux is nullifiedso that the plunger and valve are raised by the field produced byenergization of coils 62 and 64.

Another embodiment of the invention is shown in FIG. 3, and suchembodiment includes an actuator rod 114 which is supported for slidablemovement in a central bore of a magnetic housing 115 composed of anupper magnetic member 116 and a lower magnetic member 118. The membersare joined to one another at a seam of 120. Attached to actuator rod 114is a magnetic plunger 122 which is movable from a lower position, asshown in FIG. 3, against magnetic member 1 18 to an upper positionagainst upper magnet member 116. Fixed within the housing formed bymagnetic members 116 and 118 is a radially poled cylindric shapedpermanent magnet 124 in the central opening of which is fixed a magneticcylinder 126, magnetic cylinder 126 has an inner surface which confrontsthe outer surface of plunger 122. Non-magnetic cylindric guide bushings128 and 130 are placed at opposite ends of magnetic member 126 to guideplunger 122 throughout its travel and to impart rigidity to thestructure. Supported above permanent magnet 124 within upper magnetichousing member 116 is an annular shaped coil 132 which has conventionalelectrical terminations (not shown) on the exterior of housing 115.

Plunger 122 is latched in the position shown in FIG. 3 by flux thatfollows a path indicated at 134 in the figure. The flux originates inpermanent magnet 124 and traverses magnetic cylinder 126, plunger 122,and magnetic housing number 118. When it is desired to move the plunger122 upward, coil 132 is energized by supplying power thereto. Becausemagnetic member 116 has a higher saturation and permeability thanmagnetic member 118, the force produced by energizing coil 132 issufficient to overcome the latching flux indicated at 134. When theplunger 132 reaches the upper position, and closes the upper air-gap,the plunger will remain in such position even after removal of powerfrom coil 132 because of the latching flux produced by permanent magnet124 which traverses magnetic cylinder 126, plunger 122 and uppermagnetic housing member 116. When it is desired to effect downwardmovement of plunger 122, coil 132 is pulsed with a reverse polaritysignal which generates a magnetic flux at the upper air-gap that nullsthe flux produced by permanent magnet 124 and switches the permanentmagnet flux to the lower air-gap thereby generating a net downwardforce.

Varaitions of the design shown in FIG. 3, include splitting the plungerat its axial mid-plane and connecting actuator rod 114 to the lowerplunger section thereby decreasing the required coil current andstroking force without decreasing the latching force and by placing anarrow non-magnetic ring at seam 120 between upper magnetic member 116and lower magnetic member 118 to alter the latching force.

Still another embodiment of the invention is shown in FIG. 4. Suchembodiment includes a cylindric magentic housing member 136 in theopposite ends of which are fixed magnetic members 138 and 140 whichtogether form magnetic housing for the embodiment. Within the housing isa radially poled cylindric permanent magnet 142 in the center opening ofwhich is fixed a cylindric magnetic sleeve 144. Within magnetic endmember 140 is a lower coil 148. Non-magnetic sleeves and 152 span thespace between the ends of cylindric sleeve 114 and magnetic end pieces138 and 140 so as to afford rigidity to the structure and to form afluid-tight chamber within the structure. A tube 154 communicates withone end of the chamber and a tube 156 communicates with the other end ofthe chamber. Within the chamber is supported a spool shaped plunger 157formed by a central spindle 158 on opposite ends of which are cups 160and 162. Around the periphery of cups 160 and 162 are roll-sock seals164 which define a fluid tight chamber between end flanges 160 and 162and cylindrical sleeve 144. Such chamber is filled with ferromagneticfluid 166 which is typically composed of finely ground ferromagneticparticles suspended in a suitable liquid medium. Thus the fluidfunctions in a manner equivalent to the solid magnetic plungers referredto in the previously described embodiments.

Although the plunger is shown in the mid-point in FIG. 4, it resides atone or the other extremes of movement, i.e. either with cups 160 againstthe inner surface of magnetic end piece 140. Energization of coils 146and 148 nullify the latching flux and cause movement of the plunger tothe opposite end in a manner substantially identical to that describedabove in connection with FIG. 2, for example. Ferromagnetic fluid 166 iscontained within the plunger and the plunger is coupled to a load by afluid which reciprocally flows through tubes 154 and 156. The forceoutput of the ferromagnetic latching actuator of FIG. 4, which is afluid pressure force, is lower than that for an equally sized solidplunger owing to the lower saturation value of ferromagnetic fluid 166.In addition, the force produced in the ferromagnetic fluid is a bodyforce or fluid pressure. This effect may be used directly to pumpferromagnetic fluids, accomplished by removing roll-sock seals 164 andadding non-magnetic inlet and outlet check valves within tubes 154 and156.

The present invention can be embodied in an apparatus which providesstepped rotary motion, an example of such embodiment being shown inFIGS. and 5A. Such embodiment includes a stator housing 169 that isformed by a cylindric magnetic member 170, the upper axial end of whichis closed by an outer magnetic member 172 and an inner magnetic member174, and the lower end of which is closed by an outer magnetic member176 and an inner magnetic member 178. Inner magnetic members 174 and 178are centrally bored and support bearings 180 which in turn support ashaft 182 for rotation within the housing. Shaft 180 is provided withspherical splines 184 at a location intermediate inner magnetic endpieces 174 and 178. A rotor 186 has a complementally shaped hub 188which cooperates with spherical splines 184 to cause shaft 182 and rotor186 to rotate in unison and to permit the rotor to rock or nutate withrespect to shaft 182.

Rotor 186 includes a non-magnetic central portion 190 attached to hub188, an inner magnetic ring 192 an outer magnetic ring 196, and a ringshaped pennanent magnet 198 which is supported between the inner andouter magnetic rings. A non magnetic ring gear 200 is attached to thebottom of permanent magnet ring 198 and cooperates with a second ringgear 202 which is rigid with lower stationary ring 176. As will appearin more detail hereinafter ring gears 202 and 204 have a differentnumber of teeth so that rotor 186 incrementally rotates in response tonutation thereof.

The end members of stator 169 are excised to receive a plurality ofannular electric coils, there being in the embodiment shown in FIGS. 5and 5A twelve such coils, six of which are identified by referencenumerals 204, 206, 208, 210, 212 and 214. Corresponding upper coils ofequivalent construction and location are in opposition to the lowercoils; two of such upper coils appear in FIG. 5 and are designated byreference numerals 208a, and 2140. The above enumerated electric coilsare provided with exterior terminations (not shown) for effectingattachment to suitable control circuitry.

It is preferred that nutating gear 200 has a number of teeth thatexceeds by l the number of teeth on fixed gear 202. By way of example,if nutating gear 200 has 101 teeth, fixed gear 202 has I00 teeth. Theconsequence of such relationship is that each time rotor 186 wobbles ornutates, it will be advanced l/IOOth ofa circle.

When no power is supplied to the coils 204-214, 186 assumes a positionas shown in FIG. 5 and is there latched by magnetic flux produced bypermanent magnet 198. The two latching paths are schematicallydesignated in FIG. 5 by broken lines 216 and 218. It will be noted thatthe flux path designated by line 216 passes through the center of coil208A and that the flux path identified by line 218 passes through thecenter of coil 214.

The operation of the embodiment of the invention shown in FIGS. 5 and 5Acan be understood by assuming that coil 208A is pulsed to produce a fluxthat opposes and nullifies the flux identified by line 216 and that coil214 is pulsed to produce a flux that opposes and nullifies the permanentmagnet flux identified by line 218. Simultaneously, coils 208 and 214are pulsed in a direction to add to the permanent magnet flux producedby permanent magnet 198, so that rotor 186 will pivot or nutate in aclockwise direction as viewed in FIG. 5. As ring gear 200 meshes withring gear 202 in a region adjacent coil 208, rotor 186 is incrementallyadvanced to a position at which the teeth fully mesh. Such incrementaladvance is transmitted to shaft 182, and the load attached thereto. Inorder to advance rotor 186 another increment, the same groups of coilsare pulsed in opposite polarity whereby rotor 186 pivots or nutates in acounter-clockwise direction as in FIG. 5 and advances shaft 182 anotherincrement. As rotor 186 moves around stator 169, different combinationsof coils are pulsed and control circuitry attached or otherwiseassociated with shaft 182 switches the current supply to the appropriatecombination of coils. Thus, it will be seen that by alternatelyreinforcing and nullifying the flux produced by permanent magnet ring198, shaft 182 can be caused to advance a precise amount and the shaftwill remain in position after termination of all power to the coilsbecause of the latching flux produced by permanent magnet ring 198.

In order to advance shaft 182 through a smaller increment that thatreferred to in the preceding paragraph, adjacent rathr thandiametrically opposed coil pairs can be pulsed. For example, pulsingcoils 208A and 214 to null the permanent magnet flux and coils 210A and204 to reinforce the permanent magnet flux causes rotor 186 to advancean increment one-third that of the above example (the rotor nutatesthrough only 60, the angular space between adjacent coils).

Another version of the invention is shown in FIGS. 6A, 6B and 6C. Suchembodiment includes a rotor 220 which is fastened to a shaft 222. Shaft222 is supported for rotation in a stator housing 224 by means ofsuitable bearings 226. The rotor 222 includes 12 permanent magnets 228which are uniformally spaced about the periphery of the rotor and arespaced from one another by wedge shaped magnetic members 230. Arrows 232indicate the direction in which the permanent magnets are polarized andit will be noted that each magnet is polarized opposite from the twomagnets adjacent to it. It will be further noted that the peripheralextent of each magnetic member 230 is equal to the peripheral extent ofeach permanent magnet 228 so that the rotor has 24 stations of 15 each.

Stator 224 is composed of two sections each of which is equal toapproximately one-half the axial extent of permanent magnets 228. Thestator sections are indicated generally in FIG. 6A by reference numerals232 and 234. Each stator section is identical in construction but whenthey are assembled they are offset circumferentially from one another.Stator 232, for example, includes a magnetic ring 236 on the inneropening of which are twelve uniformly spaced excisions 238. Theexcisions have a peripheral extent equal to that of permanent magnets228 in rotor 220. Consequently, between each adjacent excision 238 is amagnetic tooth face 240 which has a 15 extent and cooperates withmagnetic member 230 in the rotor to form a latching path. Wound aroundring 236 and within each excision 238 is an associated coil 242; anouter magnetic housing 244 has inwardly facing excisions 246 so that theouter magnetic member can be assembled in the position shown in FIG. 6A.Corresponding parts of stator section 234 are identified by the samereference numerals used in conjunction with stator section 232, exceptthat those elements that form a part of stator section 234 are primed.That is to say, stator section 234 is composed of an inner ring 236', anouter ring 244 and a plurality of electric coils 242. The coils areperipherally spaced from one another by tooth faces 240.

The embodiment of FIGS. 6A6C operates as follows:

The rotor is latched in the position shown in the drawings bycooperation between the rotor and stator section 232. The path of thelatching flux is indicated by line 248 in the drawing which it will benoted originates from permanent magnet 228 and passes through a wedgeshaped magnetic member 230, stator ring 236, another wedge shaped rotormember 230 and back to the permanent magnet. As can be seen in FIG. 6Athis magnetic flux path passes through the inner opening of a coil 242.It will be noted on the left side of FIG. 6A, which depicts the relativeposition between the rotor and stator section 234, that there is ahigher reluctance air-gap between wedge shaped rotor members 230 andmagnetic stator ring 236' because the wedge shaped members are oppositecoils 242'. When it is desired to advance the rotor, all coils 242 areenergized so as to oppose and nullify the flux exemplified by line 248.At the same time coils 242' in stator section 234 are energized to addto the flux produced by permanent magnets 228 whereby the rotor advancesone step, equal to 15 in the embodiment shown in FIG. 6A. Aftertermination of the current to the coils the rotor will be magneticallylatched in its new position by cooperation with the permanent magnetsand stator section 234. Repetition of the above procedures advancesrotor 220 another increment and between each step the rotor is latchedin a position by cooperation of the permanent magnets and the magneticmembers in the rotor and in the stator.

The circuitry for energizing the coils employed in the variousembodiments described hereinabove, can take many forms. A suitablecurrent source is shown in FIG. 7. The circuit includes a positive powerinput terminal 320 and a negative power input terminal 322 which areconnected to any suitable direct currentpower source. A conventionalfuse 324 is provided for protecting the circuit and the actuator towhich it is connected from overloads. In series with one of the inputleads, e.g., that connected to negative input terminal 322, is a powertransistor to 326 the base or trigger lead of which is connected to aterminal 328. The output of the circuit is connected to output terminals330 and 332. Such terminals are connected to opposite corners of abridge circuit formed by four SCRs 334, 336, 338 and 340. The triggerelectrodes of SCR's 334 and 338 are commonly connected to a controlterminal 342 and the trigger terminals of SCR's 336 and 340 are commonlyconnected to a terminal 344. When the circuit of FIG. 7 is employed tocontrol the embodiment of the invention shown in FIGS. lA-lD, coils 22and 24 are connected in series between output terminals 330 and 332.

The operation of the circuit of FIG. 7 in conjunction with theembodiment of the invention shown in FIG. 1A is as follows: With DCpower connectted to input terminals 320 and 322, a bias is applied toone or the other of input terminals 342 and 344, for example, inputterminal 342. This causes SCRs 334 and 338 to conduct. Trigger terminal328 is then pulsed for a suitable duration and the positive side of theDC power source is thereby switched to terminal 330 and the negativeside of the power source is switched to output terminal 332. Accordinglythe coils 22 and 24 are energized so that one opposes and nullifies thelatching flux afforded by the permanent magnet and the other enhances oris added to such flux. In consequence of this, the moving part of theactuator is switched to the opposite position. Thereafter, the controlsignal is disconnected from input terminal 342 and connected to terminal344 and when another actuation of the actuator is required, a suitablepulse is supplied to control terminal 328. With a circuit in thisconfiguration, the positive side of the DC power source is connected tooutput terminal 332 and the negative side is connected to outputterminal 330, whereupon the actuator returns to the original position.

Thus it will be seen that the present invention provides an extremelysimple and efficient electromagnetic latching actuator. The actuator iscapable of extremely high forces without undue consumption of power.Moreover, the actuator is passively latched in a given position withoutconsuming any power from exterior sources because, in each case, thepermanent magnet is poled in such a direction that the magnetic lengththereof is less than the square root of the cross section of themagnetic path across which the flux is active. The invention can beincorporated into reciprocating, rotary, or other forms of mechanicallinkages without sacrificing the advantages alluded to hereinabove.

Although several embodiments of the invention have been shown anddescribed, it will be obvious that other adaptations and modificationscan be made without departing from the true spirit and scope of theinvention.

What is claimed is:

1. In an actuator of the type that has a housing and a driving elementsupported in said housing for movement between a first position and asecond position, an improved system for controlling the movement andposition of said element with respect to said housing, said systemcomprising a first magnetic member attached to the driving element, asecond magnetic member rigid with said housing and arranged to form amagnetic circuit path with said first magnetic member, said magneticcircuit having a vairable reluctance first air-gap therein between saidfirst and second magnetic members which first air-gap is relativelysmall in said first position, a permanent magnet interposed in saidmagnetic circuit path to establish in said magnetic circuit path alatching flux for latching saiddriving element in said first positionrelative to said housing, said permanent magnet having a magnetic lengthalong the circuit path that is less than the square root of thetransverse area of the circuit path, at least one electric coil fixedwithin said housing circumscribing at least one of said magneticmembers, said coil producing a magnetic flux in resonse to electricalexcitation thereof that opposes and nullifies the latching flux producedin said magnetic circuit by said permanent magnet to permit movement ofsaid driving element relative to said housing away from said firstposition thereby to increase the reluctance of said first air-gap, and athird magnetic member spaced from said second magnetic member andcorresponding to said second position and being arranged to form withsaid permanent magnet and said first magnetic member a second latchingflux path for latching said driving element in said second position.

2. An actuator according to claim 1 wherein said permanent magnet isattached to first magnetic member for movement therewith.

3. An actuator according to claim 1 wherein said permanent magnet isattached to said housing and said second magnetic member.

4. An actuator according to claim 1 wherein said permanent magnet is ofannular form and defines a central opening and wherein said firstmagnetic member has a shape substantially similar to said opening andresides therein to define a low reluctance path therebetween.

5. In an electromagnetic latching actuator of the class having permanentmagnet means for producing magnetic flux in at least two variablereluctance parallel magnetic circuits, electric coil means for switchingsaid permanent magnet flux between said magnetic circuits, a movablehigh permeability element that flux links said magnetic circuits andthat is moved by said flux switching so as to vary reluctance in saidmagnetic circuits, and means for attaching movable objects to saidmovable element, the improvement comprising means forming at least twovariable reluctance magnetic circuits with variable air-gaps in which apermanent magnet having a short magnetic length and a large magneticarea is in series with said magnetic circuits, at least one electriccoil means which alternately switches the permanent magnet induced fluxbetween said magnetic circuits by being energized with alternatingelectrical voltage polarity without switching flux direction in thepermanent magnet, and a movable high permeability element that fluxlinks said magnetic circuits and that is moved by said flux switching soas to increase the reluctance of the magnetic circuit to which it waslatched to and to decrease the reluctance of the magnetic circuit towardwhich it is attracted and subsequently latched to with said latchingprovided solely by the permanent magnet induced flux so that saidmovable element with said attached movable objects is unlatched from oneposition and is attracted to and passively latched at another position.

6. An electromagnetic latching actuator in accordance with claim 5comprising two parallel magnet circuits with variable air-gaps in whicha radially poled toroidal permanent magnet having a short magneticlength and a large magnetic area is in series with said magneticcircuits, an electric coil for each magnetic circuit which alternatelyswitches the permanent magnet induced flux between said magneticcircuits without switching flux direction in the permanent magnet, thetwo electric coils being series energized with alternating voltagepolarity, a movable high permeability element that flux links saidmagnetic circuits and that is moved by said flux switching so as toincrease the reluctance of the magnetic circuit too which it was latchedto and to decrease the reluctance of the magnetic circuit toward whichit is attracted and subsequently latched to with said latching providedsolely by the permanent magnet induced flux.

7. An electromagnetic latching actuator in accordance with claim 6 inwhich the permanent magnet is integral with the movable highpermeability element.

8. An electromagnetic latching actuator in accordance with claim 6 inwhich the permanent magnet is integral with the common segment of thetwo stationary parallel magnetic circuits.

9. An electromagnetic latching actuator in accordance with claim 5comprising two parallel magnetic circuits with variable air-gaps inwhich a radially poled toroidal permanent magnet having a short magneticlength and a large magnetic area is in series with said magneticcircuits, an electric coil mounted in one magnetic circuit hichalternately switches the permanent magnet induced flux between saidmagnetic circuits without switching flux direction in the permanentmagnet, a movable high permeability element that flux links saidmagnetic circuits and that is moved by said flux switching so as toincrease the reluctance of the magnetic circuit to which it was latchedand to decrease the reluctance of the magnetic circuit toward which itis attracted and subsequently latched to with said latching providedsolely by the permanent magnet induced flux.

10. An electromagnetic latching actuator in accordance with claim 5comprising a stator including at least three pairs of variablereluctance parallel magnetic circuits arranged in a circular array witheach said circuit pair having two electric coils with one coil of eachsaid circuit pair mounted in a planar circumferential circular array andwith the second coil of each said circuit pair colinear with said firstcoil and mounted in a planar circumferential circular array parallel toand concentric with the first planar circular array but separated by afixed axial distance wherein fixed axial dis tance is maintained by anannular ring of high permeability material and a rotor including aradially poled permanent magnet segment having a short magnetic lengthand a large magnetic area and means attached to said permanent magnetfor forming a common return magnetic circuit in series with saidmagnetic circuit pairs and within said fixed axial distance, said rotorbeing in the form of a nutating wheel that acts as the movable highpermeability element which is splined to and nutates about a splinedshaft whose axis is normal to plane of said circular array, so that saidwheel nutates in response to the sequential energization ofdiametrically opposite said electric coils so as to nutate said nutatingwheel thereby rotating said output shaft.

11. An electromagnetic latching actuator in accordance with claim 10 inwhich said nutating wheel has a toothed flange and said stator has agear thereby forming a nutating gear which nutates by engaging saidwheel with said gear, said gear being coplanar to said circular arrayand said gear having a different number of teeth than said nutatingwheel,

12. An electromagnetic latching actuator in accordance with claim 5comprising a stator that includes first and second substantiallyidentical sections, each said section including a toothed ring havinginward extending teeth that are of uniform circumferential extent andare spaced from one another by an equal extent to define a space betweeneach tooth that is equal in circumferential extent to that of the tooth,an electric coil disposed in each space and circumscribing the ring sothat a magnetic path between adjacent teeth passes through the portionof the ring that is circumscribed by said coil, said first and secondstator sections being joined to one another so that the coils of firstsection reside in axial alignment with the teeth in the second section,and a rotor supported for rotation within the toothed rings of saidstator, said rotor having a plurality of permanent magnets at theperiphery thereof, said permanent magnets each having a circumferentialextent equal to that of the teeth on said stator and an axial extent atleast as great as that of the combined stator sections, a magnetic wedgeshaped spacer between each said permanent magnet, said spacer having acircumferential extent equal to that of the permanent magnets and theteeth, so that opposite energization of the coils in the first statorsection and the coils in the second stator sections causes rotation ofsaid rotor by an increment equal to the circumferential extent of theteeth.

13. An actuator in accordance with claim 5 in combination with a valvebody, means for connecting the valve body to said moveable element, avalve seat mounted in alignment with said valve body and post tionedwith respect thereto so that the valve body is latched against said seatat one position of the actuator and latched in spaced apart relation tothe seat in the other position of the actuator.

14. An actuator according to claim 13 wherein said valve body connectingmeans comprises a tubular resilient member, said tubular member having aplurality of diametrically opposed pairs of excisions, the excisions ofadjacent pairs being circumferentially offset from one another.

15. An actuator according to claim 13 in combination with a rod attachedto said moveable element, a conductive spring washer attached to saidrod, a first pair of contacts disposed so as to be bridged by saidspring washer at one position of said actuator and a second pair ofcontacts disposed so as to be bridged by said spring washer at the otherposition of said actuator.

16. An actuator according to claim 5 in combination with a rod attachedto said moveable element, a conductive member attached to aid rod, afirst pair of contacts disposed so as to be bridged by said conductivemember at one position of said actuator and a second pair of contactsdisposed so as to be bridged by said conductive member at the otherposition of said actua-

1. In an actuator of the type that has a housing and a driving elementsupported in said housing for movement between a first position and asecond position, an improved system for controlling the movement andposition of said element with respect to said housing, said systemcomprising a first magnetic member attached to the driving element, asecond magnetic member rigid with said housing and arranged to form amagnetic circuit path with said first magnetic member, said magneticcircuit having a vairable reluctance first air-gap therein between saidfirst and second magnetic members which first air-gap is relativelysmall in said first position, a permanent magnet interposed in saidmagnetic circuit path to establish in said magnetic circuit path alatching flux for latching said driving element in said first positionrelative to said housing, said permanent magnet having a magnetic lengthalong the circuit path that is less than the square root of thetransverse area of the circuit path, at least one electric coil fixedwithin said housing circumscribing at least one of said magneticmembers, said coil producing a magnetic flux in resonse to electricalexcitation thereof that opposes and nullifies the latching flux producedin said magnetic circuit by said permanent magnet to permit movement ofsaid driving element relative to Said housing away from said firstposition thereby to increase the reluctance of said first air-gap, and athird magnetic member spaced from said second magnetic member andcorresponding to said second position and being arranged to form withsaid permanent magnet and said first magnetic member a second latchingflux path for latching said driving element in said second position. 2.An actuator according to claim 1 wherein said permanent magnet isattached to first magnetic member for movement therewith.
 3. An actuatoraccording to claim 1 wherein said permanent magnet is attached to saidhousing and said second magnetic member.
 4. An actuator according toclaim 1 wherein said permanent magnet is of annular form and defines acentral opening and wherein said first magnetic member has a shapesubstantially similar to said opening and resides therein to define alow reluctance path therebetween.
 5. In an electromagnetic latchingactuator of the class having permanent magnet means for producingmagnetic flux in at least two variable reluctance parallel magneticcircuits, electric coil means for switching said permanent magnet fluxbetween said magnetic circuits, a movable high permeability element thatflux links said magnetic circuits and that is moved by said fluxswitching so as to vary reluctance in said magnetic circuits, and meansfor attaching movable objects to said movable element, the improvementcomprising means forming at least two variable reluctance magneticcircuits with variable air-gaps in which a permanent magnet having ashort magnetic length and a large magnetic area is in series with saidmagnetic circuits, at least one electric coil means which alternatelyswitches the permanent magnet induced flux between said magneticcircuits by being energized with alternating electrical voltage polaritywithout switching flux direction in the permanent magnet, and a movablehigh permeability element that flux links said magnetic circuits andthat is moved by said flux switching so as to increase the reluctance ofthe magnetic circuit to which it was latched to and to decrease thereluctance of the magnetic circuit toward which it is attracted andsubsequently latched to with said latching provided solely by thepermanent magnet induced flux so that said movable element with saidattached movable objects is unlatched from one position and is attractedto and passively latched at another position.
 6. An electromagneticlatching actuator in accordance with claim 5 comprising two parallelmagnet circuits with variable air-gaps in which a radially poledtoroidal permanent magnet having a short magnetic length and a largemagnetic area is in series with said magnetic circuits, an electric coilfor each magnetic circuit which alternately switches the permanentmagnet induced flux between said magnetic circuits without switchingflux direction in the permanent magnet, the two electric coils beingseries energized with alternating voltage polarity, a movable highpermeability element that flux links said magnetic circuits and that ismoved by said flux switching so as to increase the reluctance of themagnetic circuit too which it was latched to and to decrease thereluctance of the magnetic circuit toward which it is attracted andsubsequently latched to with said latching provided solely by thepermanent magnet induced flux.
 7. An electromagnetic latching actuatorin accordance with claim 6 in which the permanent magnet is integralwith the movable high permeability element.
 8. An electromagneticlatching actuator in accordance with claim 6 in which the permanentmagnet is integral with the common segment of the two stationaryparallel magnetic circuits.
 9. An electromagnetic latching actuator inaccordance with claim 5 comprising two parallel magnetic circuits withvariable air-gaps in which a radially poled toroidal permanent magnethaving a short magnetic length and a large magnetic area is in serieswith said magnetic circuits, an electric Coil mounted in one magneticcircuit hich alternately switches the permanent magnet induced fluxbetween said magnetic circuits without switching flux direction in thepermanent magnet, a movable high permeability element that flux linkssaid magnetic circuits and that is moved by said flux switching so as toincrease the reluctance of the magnetic circuit to which it was latchedand to decrease the reluctance of the magnetic circuit toward which itis attracted and subsequently latched to with said latching providedsolely by the permanent magnet induced flux.
 10. An electromagneticlatching actuator in accordance with claim 5 comprising a statorincluding at least three pairs of variable reluctance parallel magneticcircuits arranged in a circular array with each said circuit pair havingtwo electric coils with one coil of each said circuit pair mounted in aplanar circumferential circular array and with the second coil of eachsaid circuit pair colinear with said first coil and mounted in a planarcircumferential circular array parallel to and concentric with the firstplanar circular array but separated by a fixed axial distance whereinfixed axial distance is maintained by an annular ring of highpermeability material and a rotor including a radially poled permanentmagnet segment having a short magnetic length and a large magnetic areaand means attached to said permanent magnet for forming a common returnmagnetic circuit in series with said magnetic circuit pairs and withinsaid fixed axial distance, said rotor being in the form of a nutatingwheel that acts as the movable high permeability element which issplined to and nutates about a splined shaft whose axis is normal toplane of said circular array, so that said wheel nutates in response tothe sequential energization of diametrically opposite said electriccoils so as to nutate said nutating wheel thereby rotating said outputshaft.
 11. An electromagnetic latching actuator in accordance with claim10 in which said nutating wheel has a toothed flange and said stator hasa gear thereby forming a nutating gear which nutates by engaging saidwheel with said gear, said gear being coplanar to said circular arrayand said gear having a different number of teeth than said nutatingwheel.
 12. An electromagnetic latching actuator in accordance with claim5 comprising a stator that includes first and second substantiallyidentical sections, each said section including a toothed ring havinginward extending teeth that are of uniform circumferential extent andare spaced from one another by an equal extent to define a space betweeneach tooth that is equal in circumferential extent to that of the tooth,an electric coil disposed in each space and circumscribing the ring sothat a magnetic path between adjacent teeth passes through the portionof the ring that is circumscribed by said coil, said first and secondstator sections being joined to one another so that the coils of firstsection reside in axial alignment with the teeth in the second section,and a rotor supported for rotation within the toothed rings of saidstator, said rotor having a plurality of permanent magnets at theperiphery thereof, said permanent magnets each having a circumferentialextent equal to that of the teeth on said stator and an axial extent atleast as great as that of the combined stator sections, a magnetic wedgeshaped spacer between each said permanent magnet, said spacer having acircumferential extent equal to that of the permanent magnets and theteeth, so that opposite energization of the coils in the first statorsection and the coils in the second stator sections causes rotation ofsaid rotor by an increment equal to the circumferential extent of theteeth.
 13. An actuator in accordance with claim 5 in combination with avalve body, means for connecting the valve body to said moveableelement, a valve seat mounted in alignment with said valve body andpositioned with respect thereto so that the valve body is latchedagainSt said seat at one position of the actuator and latched in spacedapart relation to the seat in the other position of the actuator.
 14. Anactuator according to claim 13 wherein said valve body connecting meanscomprises a tubular resilient member, said tubular member having aplurality of diametrically opposed pairs of excisions, the excisions ofadjacent pairs being circumferentially offset from one another.
 15. Anactuator according to claim 13 in combination with a rod attached tosaid moveable element, a conductive spring washer attached to said rod,a first pair of contacts disposed so as to be bridged by said springwasher at one position of said actuator and a second pair of contactsdisposed so as to be bridged by said spring washer at the other positionof said actuator.
 16. An actuator according to claim 5 in combinationwith a rod attached to said moveable element, a conductive memberattached to aid rod, a first pair of contacts disposed so as to bebridged by said conductive member at one position of said actuator and asecond pair of contacts disposed so as to be bridged by said conductivemember at the other position of said actuator.